The present invention relates to a thickness detector for detecting a thickness of a paper sheet or the like.
In a conventional thickness detector using a belt to convey a paper sheet a roller having a fixed shaft and a movable roller having a support structure are used. These rollers are movable vertically and are paired in opposition to each other. When a paper sheet or the like passes between the pair of rollers, a displacement amount of the movable roller is detected as a thickness of the object. In this case, a plurality of pairs of rollers are disposed to measure a thickness distribution of the object in the direction perpendicular to the conveyance direction of the object.
In a conventional apparatus using another detection method, optical range-meters are provided at predetermined intervals above and below an object to be measured, opposed to each other. The distance to the object is measured by each of the optical range-meters, to detect the thickness thereof.
In the above-described method of detecting a thickness by a displacement of a roller, the roller has a certain weight, and therefore, a paper sheet or the like sometimes jams into the roller. Also, this method achieves only a low response ability to a rapid change caused when the top end of an object running enters into between rollers, when the rear end of the object comes out from between the rollers, or when a surface onto which a tape is adhered passes. Therefore, the detection speed is limited. Consequently, there has been a demand for a detector capable of detecting the thickness of an object being conveyed at a high speed with high accuracy.
In case of detecting a thickness distribution in the widthwise direction by disposing pairs of rollers, the rollers cannot be provided tightly due to roller support members and the like. It is therefore difficult to raise the resolution in the widthwise direction. Further, there is a problem that a swing of an object may be measured as displacement of the roller so that the detection accuracy is deteriorated when an object swings in the thickness direction while running. From the view point of manufacture, the manufacturing cost is high since the processing accuracy of the rollers and roller support members must be raised to reduce rattling during rotation of the rollers.
In the above-described method of detecting a thickness using optical range-meters, the amount of reflection light changes depending on the coloring of an object to be measured, and therefore, errors are included in the thickness measurement results. An optical range-meter which is not influenced by the coloring of an object is expensive, and has a large outer size which restricts the space where the range finder can be installed. Therefore, there has been a demand for a low priced thickness detector, which is not influenced by the coloring of an object to be measured and which does not occupy a large installation space.